1. Technical Field
The present invention relates to a piezoelectric film laminate including a lithium tantalate substrate and a lead zirconate titanate niobate layer, and a device including the piezoelectric film laminate.
2. Related Art
A demand for surface acoustic wave devices has rapidly increased along with a remarkable development in the communication field. The development of the surface acoustic wave device is trending toward a reduction in size and an increase in efficiency and frequency. This requires a higher electromechanical coupling coefficient, more stable temperature properties, and a higher surface acoustic wave propagation velocity.
A surface acoustic wave device having a structure in which interdigital transducers (IDT) are formed on a piezoelectric single crystal has been used. As typical examples of the piezoelectric single crystal having a high electromechanical coupling factor k2, which may be used for an RF filter for which an increase in band and a decrease in loss in the passband are required, lithium niobate (hereafter LiNbO3) and lithium tantalate (hereafter LiTaO3) have been used. For example, a Y-cut Z-propagation LiNbO3 substrate (k2=4.8%), a 127.8° Y-cut X-propagation LiNbO3 substrate (k2=5.5%), a X-cut 112.2° Y-propagation LiTaO3 substrate (k2=0.75%), Y-cut Z-propagation LiTaO3 substrate (k2=0.66%), and a 36° Y-cut X-propagation LiTaO3 substrate (k2=0.66%) are often used. Among them, the 36° Y-cut substrate is mainly used currently for RF filters because a high electromechanical coupling factor (k2) and a low temperature coefficient of frequency (TCF) are both satisfied.
In a surface acoustic wave device using a piezoelectric single crystal substrate, properties such as the electromechanical coupling factor (k2), temperature coefficient, and speed of sound are values specific to the material and are determined by the cut angle and the propagation direction. Properties of the device are expected to be improved, by combining favorable properties among the speed of sound, electromechanical coupling factor (k2), and temperature properties, through depositing a piezoelectric thin film on a substrate and controlling the film thickness of the piezoelectric thin film. In particular, by depositing a piezoelectric thin film having a high electromechanical coupling factor (k2) on a piezoelectric single crystal substrate, the original electromechanical coupling factor of the piezoelectric single crystal substrate is expected to be made higher. An example of related art is described in Jpn. J. Appl. Phys. Vol. 37 (1998) 2929.